Fix escaping error in blog demo

Closes #726.
Ignore negative return values from CurlMulti.timeout.

pycurl has a wraparound bug that can turn very large timeouts into
negative numbers.

Closes #712.
Parse if-modified-since timestamps without going through time_t or local time.

This fixes a bug on windows in which mktime cannot work with times before
the epoch.

Closes #713.